1. Field of the Invention
The present invention relates generally to a process and an apparatus for use in etching the outer surface of a metal member, such as for example, a bar, rod, pipe or tube made of, for example, zirconium or zirconium alloy, and more particularly to a process and an apparatus which facilitates the automatic etching of a metal member, such as, for example, a bar, rod, pipe or tube with improvements in the resulting surface condition.
2. Description of the Prior Art
Heretofore, an etching treatment has been widely used for a metal member, such as, for example, a bar, rod, pipe, or tube in an attempt to remove defects within or upon the surface of the metal member and to obtain a desired surface condition by etching the outer surface of the metal member with acid solutions, followed by neutralization and water rinsing. Typified by those attempts is a dipping etching process which employs a plurality of tanks, however, such a process poses many shortcomings in that even in the case that a plurality of stainless steel rods or pipes are simultaneously dipped within a tank at the same time, there is required many man-hours for performing the operations of processing such pipes or rods from one tank to another, and that in the case of etching special type metal rods or pipes, such rods or pipes should be dipped individually. This is particularly true with the case of metal members, such as, for example, a rod, pipe or tube, made of, for example, zirconium or zirconium alloy, or titanium or titanium alloy.
The aforenoted special-type metal members, which require a smooth surface condition, such as for example, those members made of zirconium or zirconium alloy, must be subjected to polishing after the final annealing heat treatment, and then to etching of its outer surface with an acid solution, such as, for example, a nitric acid solution, hydrofluoric acid solution, or the like, in order to obtain a desired mirror-finish surface for the final product. In this case, however, the portion of the metal pipe which remains idle or non-movable within the etching acid solution, develops pits, acid stains, gouges, or other non-uniform areas upon its resulting surface. In addition, the metal pipe must be placed within a neutralizing liquid immediately subsequent to the etching operation, within which, if the dipping time of the metal pipe is excessively long, there then results non-uniform surface areas. From this viewpoint, etching of a plurality of pipes at the same time is virtually impossible.
Furthermore, in the instance that the pipes should be subjected to an etching process utilizing two types of acids, such as, for example, a concentrated acid and a weak acid, the duration of the dipping periods, for example, are specified as follows: weak acid (90 seconds).fwdarw.concentrated acid (30 seconds).fwdarw.neutralization (10 seconds).fwdarw.water rinsing, and such steps should be carried out continuously. Even in the instance of using a medium type or strength acid, steps similar to those noted heretofore should be followed. In the event of a deviation or discrepancy within the aforenoted steps, there results white corrosions upon the surface of the pipe during the final autoclave step. Still further, as the metal pipes have to be finished as closely as possible to ordered specifications in order to satisfy tests which will be performed by the consumer upon delivery, the metal pipes should be dipped within the acid solutions in an individual manner in order to insure obtaining or satisfying the strict requirements for quality.
The prior art etching process for a metal pipe, made of, for example, zirconium or zirconium alloy and required to have a smooth surface condition, will now be described, the same including a two-stage etching process utilizing concentrated and weak acids. According to such prior art etching processes, as shown for example, within FIG. 1, a weak acid tank 12, a concentrated acid tank 13, a neutralizing tank 14, and a water-rinsing tank 15 are serially arranged in a side-by-side fashion. Initially, a single metal pipe 11 is mounted within balance jigs 16, and subsequently, the balance jigs and pipe are disposed within the weak acid tank 12 by means of two operators a and b in accordance with a signal delivered from an operator e who monitors the dipping time. Within this process, the pipe is rotated slowly within the tank for approximately 90 seconds, and subsequently, in response to another signal of the operator e, the acid solution is discharged from the interior of the pipe by means of the two operators a and b.
The pipe is then placed, by means of operators c and d, within the concentrated acid tank 13 for a time period of several seconds, after which the pipe is rotated within the concentrated acid solution for a time period of approximately 30 seconds. Upon completion of this step, the pipe is disposed within the neutralizing tank 14, by means of operators a and b, without interruption, that is, without any substantial time lapse and with the acid solution retained within the pipe, for performance of a neutralizing treatment of approximately 10 seconds. The pipe is thereafter placed within a water rinsing tank 15 for performance of a water rinsing operation, the balance jigs 16 being removed at this time, the same being disposed upon a spacer support 17.
Accordingly, it is apparent that at least five operators a, b c, d and e are required for performance of the etching process of the inner and outer surfaces of the metal pipe 11, thus presenting unsatisfactory operational efficiency, the operators being relegated to merely manual operations. Another shortcoming with the aforenoted process is that a large quantity of acid and neutralizing liquid is required, and a noticeable deterioration of the liquids also results. In addition, the use of nitric acid, hydrofluoric acid, or the like presents safety problems with respect to the operators due to a generated acid vapor atmosphere and the risk of splashing of the acids onto the operators.
It appears that the primary factor which is responsible for the aforenoted discrepancies is a non-uniform and low flow rate or velocity of the acid solution relative to the surface of the metal pipe which contacts the solution. This type of an etching process also suffers from the aforenoted safety problems as well as difficulties enabling the continuous operation of the process, and accordingly, there arises a demand for improvements in the operational efficiency of etching processes for the outer surfaces of a metal member, such as for example a rod, pipe, or tube by automating the respective steps of the etching process.